Internal combustion engines include intake and exhaust valves that can be actuated by cam lobes of at least one camshaft. In some configurations the camshafts are constructed with sliding camshaft assemblies having multiple steps for varying the lift distance of an engine valve. For example, a two-step sliding camshaft may include a high lift cam lobe position for lifting an engine valve to a maximum distance, and a low lift cam lobe position for lifting the engine valve below the maximum lift distance.
At least one sliding camshaft actuator is fixed on an internal combustion engine for changing position between the multiple cam lobes. Particularly, at least one actuator pin of a camshaft actuator is operative to selectively engage displacement grooves configured on the periphery of camshaft barrels formed on the sliding camshaft assembly. As the camshaft assembly rotates, an actuator pin is selected to move into a displacement groove of the camshaft barrel which causes the sliding camshaft assembly to shift into a different position along the camshaft axis. When a sliding camshaft shifts position, the intake and/or exhaust valves are actuated differently in accordance with the changed cam lobe position, e.g., a sliding camshaft may move from a high lift cam lobe position to a low lift cam lobe position, which in turn will cause the engine operation to be different.
Thus, the sliding camshaft actuator is an important component in the proper operation of a VVL sliding camshaft system, particularly the actuator's pin extension into, and retraction from, the displacement grooves into the camshaft barrels. If an extended actuator pin is only partially retracted for any reason then a subsequent shift command could result in the partially retracted pin being broken off or some other damage caused to the sliding camshaft system. Thus, there is a need for a reliable means of ensuring that a partially extended actuator pin can be caused to fully retract to prevent damage to the sliding camshaft system.